Friday, March 1, 2013

I am looking at the conversion of chorismate to prephenate in Chorismate Mutase, to benchmark a hacky EFMO-RHF:MP2 method we've implemented in our group. Casper Steinmann did an adiabatic mapping of the reaction path, and we though it'd be cool to do coupled cluster single point energies on snapshots from the reaction path and some something ONIOM style.

Figure 1: Snapshot 1 from the reaction path; chorismate to prephanate

Anyways, the reaction complex contains 118 electrons, so we fired up MOLPRO2012 and started looking at the DF-LCCSD(T0)-F12a method. A name you should probably memorize from now on.

The single point energy evaluation took 3:43 hours with the VDZ-F12 basis set! Mind you, this was on only a single CPU core with 4 GB 16GB of RAM allocated, so no supercomputers were involved.

First I though the calculation had crashed because it didn't show up in the queue. My first attempt with the 3-21G basis set didn't converge because I failed to set the charge to -2, but this time around Molpro actually gave me an energy!
Next problem on my list is to calculate the good old MP2/cc-pVTZ energy I need to subtract in order to get my ONIOM results. Those are going to take about 5-10 hours on 8 cores.